The present invention relates to a polypropylene resin composition, to a process for the production of such resin composition and to uses thereof.
Polypropylene has widely been used in various fields including automobile parts, machine and electric appliances, household commodities, kitchen utensils and packaging films. However, problems have been brought about in that large-sized formed articles are difficult to obtain by, for example, extrusion molding, and in that a high speed molding can scarcely be attained, since polypropylene exhibits lower melt tension (abbreviated hereinafter sometimes as MT). Concretely, the following problems have been encountered:
(1) In blow molding, a phenomenon of xe2x80x9cdraw-downxe2x80x9d due to stretching of the parison by its own weight, causing decrease in the film thickness may be apt to occur, whereby blow molding of large-sized articles, for example, automobile parts, such as bumper and spoiler; and others, such as bottles, is rendered difficult.
(2) In the case of production of sheet or film by a calendering technique, the resulting sheet or film may often suffer from thickness irregularity and, in addition, it has a lower surface gloss.
(3) In the case of production of formed articles by extrusion molding, a high-speed molding may scarcely be practised and, in addition, large-sized extrusion-molded articles may difficultly be obtained.
(4) In the case of production of vacuum- or pressure formings from a sheet by a vacuum or pressure forming technique, large-sized molded articles are difficult to obtain and, in addition, a deep drawing may difficultly be incorporated.
(5) In the case of production of sheet or film by an inflation molding technique, a poor surface condition may often be encountered, since the baloon may often become unstable.
(6) In the case of producing stretched films, the resulting film may be apt to suffer from occurrence of so-called surging, so that an accident of film breaking upon the stretching may occur and, in addition, the resulting stretched film exhibits a low thickness accuracy.
(7) In the case of producing foamed articles, foaming with a high foaming ratio may difficultly be attained and, in addition, the cells of foamed article are large and coarse with non-uniform cell size.
In order to avoid these problems, it has heretofore been practised to employ such polypropylene reins as given below in which the melt tension is increased:
1) A polypropylene resin composition prepared by blending a polypropylene with a high-pressure low-density polyethylene or with a high-density polyethylene
2) A polypropylene resin having a widely extended molecular weight distribution
3) A modified polypropylene resin which is obtained by slightly cross-linking a polypropylene resin using a peroxide, electron irradiation or maleic acid
4) A branched long chain polypropylene resin which is obtained by introducing long chain branching upon the polymerization of propylene.
However, these prior art polypropylene resins having improved melt tension exhibit disadvantages in that the formed article produced therefrom reveals inferior appearance and/or lower transparency and in that the stiffness of the resin is insufficient, though occurence of draw-down is made scarce for all these resins. Alternatively, if the molding temperature is elevated in order to effect a high speed molding, problems may be brought about that the resin will suffer from deterioration due to increased heat evolution in the resin, causing higher trend to gel formation (fish eye formation).
In Japanese Patent Kokai Sho-59-149907 A, there is disclosed a process for producing a polypropylene resin having higher melt tension and higher stiffness with superior moldability by a two-stage polymerization. This process comprises performing a 1st stage polymerization of propylene to build up 50-85%, based on the entire weight of the final polymer product, of a polypropylene product having an intrinsic viscosity [xcex7] of 0.5-3.0 dl/g and, then, effecting a 2nd stage polymerization to build up 50-15%, based on the entire weight of the final polymer product, of a polypropylene product having an intrinsic viscosity [xcex7] of at least 9 dl/g, to thereby produce a crystalline polypropylene resin composition having, as the entire polypropylene resin composition, an intrinsic viscosity [xcex7] of 2-6 dl/g, a melt flow rate (MFR) of 0.01-5 g/10 min. and an isotactic pentad fraction of 0.940 or higher.
The polypropylene resin composition produced by this process exhibits, however, a wide molecular weight distribution, as seen, for example, from the Mw/Mn values given in Examples of the specification of this prior patent gazette in the range of 23.2-42.2, so that the moldability of this resin composition is worse, whereby the appearance of the molded articles therefrom becomes inferior. In addition, it exhibits a lower isotactic pentad fraction, as seen in Examples of the patent gazette in the range of 0.955-0.969, so that the stiffness of the resin is insufficient. Moreover, the polypropylene resin composition obtained by the above-mentioned two-stage polymerization suffers from a problem of high tendency to occurrence of gel formation which causes deterioration in the appearance of the molded article, since a polypropylene product exhibiting a low intrinsic viscosity [xcex7] is produced in the first stage polymerization and a polypropylene product exhibiting a high intrinsic viscosity [xcex7] is produced in the second stage polymerization. Furthermore, when performing the above-mentioned two-stage polymerization in a continuous way for the benefit of industrial production in order to produce a polypropylene product having a low intrinsic viscosity [xcex7] in the first stage polymerization and to produce a polypropylene product having a high intrinsic viscosity [xcex7] in the second stage polymerization, it is necessary to effect the first stage polymerization of propylene in the presence of hydrogen and to realize the second stage polymerization of propylene in the absence of hydrogen, so that it is required to reduce the excess hydrogen contained in the reaction product from the first stage polymerization as low as possible on subjecting it to the second stage polymerization and, thus, a complicated polymerization apparatus becomes necessary. There may occur a still further problem in that a sufficiently high intrinsic viscosity [xcex7] of the polypropylene product resulting from the second stage polymerization is not obtained due to the presence of the unremoved hydrogen rest, which may bring about an insufficient melt tension and insufficient stiffness.
In Japanese Patent Kokai Sho-59-172507 A, a process for producing a polypropylene resin superior in the stiffness, moldability and heat resistance by polymerizing propylene in two stages is disclosed. This process comprises producing, in one stage, 35-65%, based on the total weight of the final resin, of a polypropylene product having an intrinsic viscosity [xcex7] of 1.8-10 dl/g and an isotacticity of at least 97.5% by weight and producing, in the other stage, 65-35%, based on the total weight of the final resin, of a polypropylene product having an intrinsic viscosity [xcex7] of 0.6-1.2 dl/g and an isotacticity of at least 96.5% by weight, so as to thereby obtain a polypropylene resin composition having, as a whole, an intrinsic viscosity [xcex7] of 1.2-7 dl/g and a molecular weight distribution expressed by Mw/Mn of 6-20. However, the intrinsic viscosity [xcex7] of the polypropylene product of higher intrinsic viscosity [xcex7] side, namely, higher molecular weight side, of the polypropylene resin composition is relatively low, as seen from the values given in Examples of the above patent gazette lying in the range of 2.10-7.28 dl/g, so that a sufficient melt tension and sufficient stiffness will not be attained, resulting thereby sometimes in an inferior appearance and insufficient strength of the molded article produced therefrom.
In Japanese Patent Kokai Hei-6-93034 A (corresponding to EP 573862 A2), a crystalline polypropylene resin is disclosed, which has an MIL value of  greater than 2 g/10 min., an intrinsic viscosity [xcex7] of xe2x89xa62.8 dl/g, an Mw/Mn value of  greater than 20 and a 25xc2x0 C. xylene-insoluble matter of xe2x89xa794 and contains a fraction which has an intrinsic viscosity [xcex7] of xe2x89xa72.6 dl/g of 10-60% by weight. It is taught that this polypropylene resin can be produced by a successive polymerization comprising at least two steps and is superior in the processibility in molten state. The polypropylene resin composition described in the above patent gazette has a defect that the appearance of the extrusion-molded or blow-molded article thereof is inferior due to its lower moldability, though it develops a high melt tension, since it has an Mw/Mn value exceeding 20.
In Japanese Patent Kokai Sho-58-7439, a polypropylene resin composition is disclosed, which is composed of 30-70% by weight of a crystalline polypropylene having an intrinsic viscosity [xcex7] of 0.6-3.5 dl/g and 70-30% by weight of a crystalline polypropylene having an intrinsic viscosity [xcex7] of at least 2.5 times that of the former within the range of 5-10 dl/g and which has, as a whole, an intrinsic viscosity [xcex7] of 4-6 dl/g. It is taught that this polypropylene resin composition exhibits a superior moldability while maintaining superior mechanical properties intrinsic to crystalline polypropylene, such as stiffness, shock resistance etc., and superior physical properties, such as transparency and heat resistance, in addition to an advantageous feature of elimination of troublesome occurrence of gel formation, so that it is adapted to a hollow molding and extrusion molding. However, this polypropylene resin composition suffers from a problem that intricated process steps are required due to the necessity of melt-blending two polypropylene resins having intrinsic viscosities [xcex7] markedly different from each other, in addition to the circumstances that the molded articles produced from this polypropylene resin composition is subject to occurrence of gel formation, resulting in an inferior appearance.
An object of the present invention is to provide a polypropylene resin composition exibiting a high melt tension and superior moldability, which can be molded efficiently by a high-speed molding into scarcely deformable larger molded articles of better appearance with high stiffness.
Another object of the present invention is to provide a process which can afford to produce the above-mentioned polypropylene resin composition in an efficient and simple manner at a lower cost.
A further object of the present invention is to provide a resin composition to be used for blow-molding which has a high melt tension and is superior in the moldability and which can be molded by a high-speed molding into scarcely deformable large-sized blow-molded articles of better appearance with superior stiffness.
A still further object of the present invention is to provide a scarcely deformable blow-molded article of better appearance which is made of the above-mentioned polypropylene resin composition or of the above-mentioned resin composition to be used for blow-molding and which will scarcely suffer from occurrence of draw-down of the parison and, thus, can be produced at a high speed in an efficient manner.
A still further object of the present invention is to provide a vacuum-formed or pressure-formed article made of the above-mentioned polypropylene resin composition, which may have a large size and which has a better appearance with superior stiffness and can be molded by a high-speed molding with permission of deep drawing.
A still further object of the present invention is to provide a calendered article made of the above-mentioned polypropylene resin composition, which may have a large size and which has a better appearance, superior stiffness, superior gloss and scarce thickness irregularity and can be formed by a high-speed forming.
A still further object of the present invention is to provide an extruded article made of the above-mentioned polypropylene resin composition, wherein the said article may have a large size, allow high-speed forming and exhibit a better appearance and superior stiffness.
A still further object of the present invention is to provide a stretched film which is made of the above-mentioned polypropylene resin composition and has a superior thickness accuracy, wherein the said film may have a large size and can be obtained by a high-speed forming in a stable manner without suffering from breaking of the film during stretching.
A still further object of the present invention is to provide a film superior in the stiffness, in the appearance and in the transparency which is made of the above-mentioned polypropylene resin composition and is produced by inflation technique, wherein the said film may have a large size and can be obtained by a high-speed forming under stable formation of the baloon upon the inflation molding.
A still further object of the present invention is to provide a foamed article which is made of the above-mentioned polypropylene resin composition and which has a uniform and fine cellular structure with a high foaming ratio, wherein the said article may have a large size and can be produced in a high-speed molding.
The present invention provides for the following polypropylene resin composition and process for the production and use of such resin composition:
(1) A polypropylene resin composition comprising polypropylene as a main component and having the following characteristic features 1) to 4), namely,
1) that the melt flow rate (MFR), determined at 230xc2x0 C. under a load of 2.16 kg, is in the range of 0.01-5 g/10 min.,
2) that the content of a high molecular weight polypropylene exhibiting an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g is in the range of 15-50% by weight,
3) that the gel areal density in number is 3,000/450 cm2 or less and
4) that the molecular weight distribution, determined by gel permeation chromatography (GPC), is in the range of 6-20 for Mw/Mn and is 3.5 or higher for Mz/Mw.
(2) A polypropylene resin composition according to the above (1), wherein it has further the following feature 5), namely,
5) that the isotactic pentad fraction (mmmm fraction) determined by 13C-NMR is at least 97%.
(3) A polypropylene resin composition according to the above (1) or (2), wherein it has further the following characteristic feature 6), namely,
6) that, when dividing the area underlying under the molecular weight distribution curve on the molecular weight distribution diagram obtained by gel permeation chromatography at the maximum peak molecular weight into two halves, the ratio of the surface area SH for the higher molecular weight side half to the surface area SL for the lower molecular weight side half, namely, SH/SL, is at least 1.3 and the proportion of the area for the high molecular weight part having molecular weights of at least 1.5xc3x97106 relative to the integral surface area underlying under the entire molecular weight distribution curve is at least 7%.
(4) A polypropylene resin composition according to either one of the above (1) to (3), wherein it has further the following characteristic feature 7), namely,
7) that the melt tension (MT), determined by flow tester at 230xc2x0 C., is in the range of 5-30 g.
(5) A process for producing a polypropylene resin composition as defined in either one of the above (1) to (4), by polymerizing propylene by a multistage polymerization in at least two stages in the presence of a polymerization catalyst formed from
(a) a solid catalyst component based on titanium, containing magnesium, titanium, a halogen and an electron donor,
(b) a catalyst component based on organometallic compound and
(c) a catalyst component based on organosilicic compound having at least one group selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and derivatives of them, the said process comprising,
making up, in the first polymerization stage, a high molecular weight polypropylene product having an intrinsic viscosity [xcex7] of 8-13 dl/g up to a proportion of 15-50% by weight with respect to the total amount of the finally obtained polypropylene resin composition, by polymerizing propylene under substantial absence of hydrogen and
performing, then, in each of the second and succeeding polymerization stages, polymerization of propylene in such a manner that a polypropylene product having an intrinsic viscosity [xcex7] lower than 8 dl/g is produced and that the melt flow rate (MFR) of the finally obtained polypropylene resin composition, as a whole, will be in the range of 0.01-5 g/10 min.
(6) A process as defined in the above (5), wherein the polymerization of propylene in each polymerization stage is effected in a continuous way.
(7) A process as defined in the above (5) or (6), wherein the polymerization of propylene in the second and succeeding polymerization stages is effected using at least two polymerization reactors.
(8) A polypropylene resin composition comprising polypropylene as a main component and having the following characteristic features 1), 2), 4), 5), 7) and 8), namely,
1) that the melt flow rate (MFR), determined at 230xc2x0 C. under a load of 2.16 kg, is in the range of 0.01-20 g/10 min.,
2) that the content of a high molecular weight polypropylene exhibiting an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g is in the range of 20-50% by weight,
4) that the molecular weight distribution, determined by gel permeation chromatography (GPC), is in the range of 6-20 for Mw/Mn and is 4 or higher for Mz/Mw,
5) that the isotactic pentad fraction (mmmm fraction) determined by 13C-NMR is at least 97%,
7) that the melt tension (MT), determined by flow tester at 230xc2x0 C., is in the range of 5-30 g, and
8) that the relationship between the melt tension (MT), determined by flow tester at 230xc2x0 C., and the critical shearing rate (SRc) meets the following formula (I)
MT greater than xe2x88x924.16xc3x97Ln(SRc)+29xe2x80x83xe2x80x83(I)
xe2x80x83in which MT represents the melt tension in gram, SRc represents the critical shearing rate in secxe2x88x921 and Ln indicates the natural logarithm.
(9) A polypropylene resin composition as defined in the above (8), wherein it has further the following characteristic feature 3), namely,
3) that the gel areal density in number is 3,000/450 cm2 or less.
(10) A polypropylene resin composition for blow molding comprising polypropylene as a main component and having the following characteristic features 1), 2), 4), 5), 7) and 8), namely,
1) that the melt flow rate (MFR), determined at 230xc2x0 C. under a load of 2.16 kg, is in the range of 0.01-20 g/10 min.,
2) that the content of a high molecular weight polypropylene exhibiting an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g is in the range of 20-50% by weight,
4) that the molecular weight distribution, determined by gel permeation chromatography (GPC), is in the range of 6-20 for Mw/Mn and is 4 or higher for Mz/Mw,
5) that the isotactic pentad fraction (mmmm fraction) determined by 13C-NMR is at least 97%,
7) that the melt tension (MT), determined by flow tester at 230xc2x0 C., is in the range of 5-30 g, and
8) that the relationship between the melt tension (MT), determined by flow tester at 230xc2x0 C., and the critical shearing rate (SRc) meets the following formula (I)
xe2x80x83MT greater than xe2x88x924.16xc3x97Ln(SRc)+29xe2x80x83xe2x80x83(I)
xe2x80x83in which MT represents the melt tension in gram, SRc represents the critical shearing rate in secxe2x88x921 and Ln indicates the natural logarithm.
(11) A polypropylene resin composition as defined in either one of the above (1) to (4) and (8) and (9), which is for blow molding.
(12) A resin composition for blow molding, comprising a polypropylene resin composition defined in any one of the above (1) to (4) and (8) to (10).
(13) A blow-molded article produced by subjecting a resin composition defined in any one of the above (1) to (4) and (8) to (12) to a blow molding.
(14) A vacuum-formed or pressure-formed article produced by subjecting a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to a vacuum- or pressure forming.
(15) A calendered article produced by subjecting a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to a calendering.
(16) A foamed article produced by subjecting a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to foaming.
(17) An extrusion-molded article produced by subjecting a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to an extrusion molding.
(18) A stretched film produced by subjecting a sheet or film made of a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to a stretching.
(19) An inflation film produced by subjecting a polypropylene resin composition as defined in any one of the above (1) to (4) and (8) and (9) to an inflation molding.
In the context of this specification, a mere denotation of xe2x80x9cthe polypropylene resin composition according to the present inventionxe2x80x9d does comprehend both the first and the second polypropylene resin compositions as described below.
The First Polypropylene Resin Composition
The first polypropylene resin composition according to the present invention comprises polypropylene as a predominant component and having, for the resin composition as a whole, the following characteristic features 1), 2), 3) and 4), wherein the first polypropylene resin composition may either comprise exclusively polypropylene or comprise other resin(s) than polypropylene in a small proportion:
1) A melt flow rate (MFR), determined in accordance with ASTM D 1238 at 230xc2x0 C. under a load of 2.16 kg, in the range of 0.01-5 g/10 min., preferably 0.1-5 g/10 min., more preferably 0.3-4 g/10 min.
2) A content of a high molecular weight polypropylene having an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin (decahydronaphthalene), of 8-13 dl/g, preferably 8.5-12 dl/g, more preferably 9-11 dl/g, in the range of 15-50% by weight, preferably 15-40% by weight, more preferably 15-35% by weight.
3) An areal density of gel in number of 3,000 per 450 cm2 or less, preferably 2,500 per 450 cm2 or less, more preferably 2,000 per 450 cm2 or less.
4) A molecular weight distribution, determined by gel permeation chromatography (GPC), in the range of 6-20, preferably 8-20 for Mw/Mn (weight-average molecular weight/number-average molecular weight) and of 3.5 or higher, preferably in the range of 3.5-6 for Mz/Mw (z-average molecular weight/weight-average molecular weight).
The a real density of number of gel mentioned above is expressed by the number of gels per a unit film surface area (450 cm2) converted from the number of gels detected using a commercial gel counter on a film of 30 xcexcm thickness prepared by a T-die film-forming apparatus of 25 mmxcfx86.
A molecular weight distribution expressed by Mw/Mn of a value in the range of 6-20 and by Mz/Mw of not lower than 3.5 does mean that the first polypropylene resin composition according to the present invention has a wider distribution in higher molecular weight ranges as compared with that of conventional polypropylene resin products.
For the first polypropylene resin composition according to the present invention, preference is given for those which have, in addition to the above characteristic features 1) to 4), further the following characteristic feature 5):
5) An isotactic pentad fraction (mmmm fraction) determined by 13C-NMR of at least 97%, preferably 98.0-99.5%.
The isotactic pentad fraction (mmmm fraction) serves as a parameter of isotacticity of polypropylene, wherein the higher this value, the higher is the isotacticity. An isotactic pentad fraction of 97% or higher does indicate that the isotacticity of the polypropylene is high. The above-mentioned isotactic pentad fraction (mmmm fraction) corresponds to the proportion of the isotactic chains as the pentad unit in the polypropylene molecular chains, which is determined using 13C-NMR and which is the proportion of the number of propylene monomeric units present in each center of the sequences of 5 monomeric propylene units bound each successively by meso-coupling. This can be determined in the practice as the proportion of the mmmm peaks relative to the entire absorption peaks within the methyl carbon region in the 13C-NMR spectrum.
For the first polypropylene-based resin composition according to the present invention, preference is given also for those which has, in addition to the above characteristic features 1) to 4) or the features 1) to 5), further the following characteristic feature 6), namely,
6) that, when dividing the area underlying under the molecular weight distribution curve on the molecular weight distribution diagram obtained by gel permeation chromatography at the maximum peak molecular weight into two halves, the ratio of the surface area SH for the higher molecular weight side half to the surface area SL for the lower molecular weight side half, namely, SH/SL, is at least 1.3, preferably at least 1.35, more preferably in the range of 1.4-2, and the proportion of the area in this diagram under the molecular weight distribution curve for the high molecular weight part of molecular weights of at least 1.5xc3x97106 relative to the integral surface area underlying under the entire distribution curve is at least 7%, preferably 7.5% or higher, more preferably in the range of 9-40%.
The surface area on the high molecular weight side SH mentioned above is the surface area of the higher molecular weight side half resulting when subdividing, on the molecular weight distribution diagram, the area confined between the molecular weight distribution curve prepared using gel permeation chromatography and the axis of abscissa (molecular weight) thereof by the vertical line at the maximum peak molecular weight into two halves. The surface area SL stands for the lower molecular weight side half thereof.
The ratio of the surface area SH of the higher molecular weight side half to the surface area SL of the lower molecular weight side half (SH/SL) refers to the shape of the molecular weight distribution curve of the polypropylene product. Thus, the case of SH/SL greater than 1 corresponds to a molecular weight distribution curve in which a bulging of the curve indicating existence of polymers of higher molecular weights is present on the high molecular weight side of the curve. In the case of SH/SL less than 1, the molecular weight distribution curve has a bulging on the low molecular weight side, indicating a content of lower molecular weight polymers. In the case of SH/SL=1, the molecular weight distribution curve has a shape in which the high molecular weight side and the low molecular weight side are balanced.
The proportion of the high molecular weight side half of the polymer product corresponds to the ratio of the surface area in the molecular weight distribution diagram for the molecular weights of 1.5xc3x97106 and higher confined between the molecular weight distribution curve and the base line (the axis of abscissa; for the molecular weight), relative to the entire surface area for all the molecular weights confined between the molecular weight distribution curve and the base line. When this proportion exceeds a certain definite value, it means that a polymer fraction of molecular weights higher than 1.5xc3x97106 is present in the polypropylene resin composition. At least a part of this high molecular weight fraction consists of a polymer fraction having an intrinsic viscosity [xcex7] of 8-13 dl/g.
For the first polypropylene resin composition according to the present invention, preference is also given for those which have, in addition to the above characteristic features 1) to 4), 1) to 5) or 1) to 6), further the following characteristic feature 7):
7) A melt tension (MT), determined by flow tester at 230xc2x0 C., is in the range of 5-30 g, preferably 5-20 g.
The melt tension (MT) refers to a tension in molten state observed at 230xc2x0 C., which is determined using Flow Tester having an orifice of a diameter of 2.095 mm and a length of 8 mm by extruding the polypropylene resin composition in molten state through the orifice of flow tester at a temperature of 230xc2x0 C. at an extrusion velocity of 15 mm/min., wherein the resin strand extruded from the orifice is guided through a pulley provided with a sensor and is wound up around the pulley at a velocity of 10 m/min., in order to observe the force imposed onto the pulley.
The first polypropylene resin composition according to the present invention provides for a high melt tension and superior in the moldability and in the stiffness, since the melt flow rate thereof is in the above-identified specific range and the content of the high molecular weight polypropylene fraction is in the range mentioned above and, in addition, the molecular weight distribution value is in the above range.
The polypropylene constituting the predominant component of the first polypropylene resin composition according to the present invention may preferably be composed exclusively of the structural unit derived from propylene, though it may include other structural unit(s) derived from other comonomer(s) than propylene in a small proportion, such as 10 mole % or lower, preferably 5 mole % or lower. Such other comonomer may include, for example, xcex1-olefins other than propylene, such as ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene; vinyl compounds, such as styrene, vinylcyclopentene, vinylcyclohexane and vinylnorbornane; vinyl esters, such as vinyl acetate and the like; unsaturated organic acids and derivatives thereof, such as maleic anhydride and the like; conjugated diene compounds; non-conjugated polyenes, such as dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylenenorbornene and 5-ethylidene-2-norbornene. Among them, preference is given to ethylene and xcex1-olefins having 4-10 carbon atoms. They may be present as copolymers of two or more of them.
The first polypropylene resin component according to the present invention may contain, as a prepolymer, 0.1% by weight or less, preferably 0.05% by weight or less, of a homopolymer or copolymer of branched olefins, for example, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 3-methyl-1-hexene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 3,5,5-trimethyl-1-hexene, vinylcyclopentane, vinylcyclohexane, vinylcycloheptane, vinylnorbornane, allylnorbornane, styrene, dimethylstyrene, allylbenzene, allyltoluene, allylnaphthalene and vinylnaphthalene. Among them, special preference is given to 3-methyl-1-butene and the like.
The polypropylene constituting the first polypropylene resin composition according to the present invention may also be a block-copolymer of propylene, which is favorable due to a possible attainment of a superior impact resistance in addition to a superior stiffness, wherein special preference is given to a propylene/ethylene block-copolymer of which rubber part has an intrinsic viscosity [xcex7] of 0.5-10 dl/g.
The polypropylene product constituting the first polypropylene resin composition may preferably be produced in a multistage polymerization with two or more stages so as to contain propylene polymers of from relatively higher molecular weights to relatively lower molecular weights. In the case where the first polypropylene resin composition is constituted exclusively of polypropylene, it is preferable to produce it in a multistage polymerization with two or more stages so as to contain propylene polymers of from relatively higher molecular weights to relatively lower molecular weights in such a way that the characteristic features 1) to 4), 1) to 5), 1) to 6) or 1) to 7) described above are attained.
As a preferred process for producing the first polypropylene resin composition according to the present invention, there may be exemplified a process in which propylene is subjected solely or together with other comonomer(s) to a multistage polymerization of at least two stages in the presence of a catalyst for producing high isotactic polypropylene. Concretely, propylene is polymerized in the first stage polymerization in the presence of a polymerization catalyst constituted of (a) a solid catalyst component based on titanium comprising magnesium, titanium, a halogen and an electron donor, (b) a catalyst component based on organometallic compound and (c) a catalyst component based on organosilicic compound having at least one substituent selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and derivatives of them in substantial absence of hydrogen to produce 15-50%, preferably 15-40%, more preferably 15-35%, based on the total weight of the finally obtained entire polypropylene resin composition, of a polypropylene product of relatively higher molecular weight having an intrinsic viscosity, determined in decalin at 135xc2x0 C., of 8-13 dl/g, preferably 8.5-12 dl/g, more preferably 9-11 dl/g, whereupon a polypropylene product of relatively lower molecular weight is produced in the second and subsequent polymerization stages. The polymerization for producing the polypropylene product of relatively lower molecular weight produced in the second and the subsequent stages is adjusted in such a manner that the intrinsic viscosity (xcex7) of the polypropylene product obtained will be lower than 8 dl/g (which refers to the intrinsic viscosity (xcex7) of the entire polypropylene resin composition including all those which are produced in the stages preceding thereto) and the melt flow rate (MFR) of the finally obtained polypropylene resin composition, as a whole, will be in the range of 0.01-5 g/10 min., preferably 0.1-5 g/10 min., more preferably 0.3-4 g/10 min. For the practical way for adjusting the intrinsic viscosity (xcex7) of the polypropylene produced in the second or subsequent stage, there is no special limitation, while it is preferable to use hydrogen as the molecular weight regulator.
As the sequential order of the production, it is preferable to produce the polypropylene of relatively higher molecular weight in the first stage under substantial absence of hydrogen and to produce then, in the second or subsequent stage(s), the polypropylene of relatively lower molecular weight. While it may be possible to reverse the polymerization order, it should be necessary therefor to incorporate exhaustive elimination of the molecular weight regulator, such as hydrogen, included in the first stage reaction product before the initiation of polymerization in the second or subsequent stage(s), in order to produce a polypropylene product of relatively lower molecular weight in the first stage and to produce polypropylene product(s) of relatively higher molecular weight in the second and the subsequent stages, so that employment of an intricated apparatus becomes necessary and attainment of increase in the intrinsic viscosity [xcex7] of the polypropylene product in the second and the subsequent stages may not be easy.
The polymerization in each stage may be realized either continuously or in a batchwise process. The polymerization may be performed in a known practice, for example, by slurry polymerization or bulk polymerization. The polymerization in the second and the subsequent stages may preferably be carried out subsequently to the first stage polymerization in a continuous manner. When a batch process is employed, the multistage polymerization can be effected in one single reactor.
While it is favorable to carry out the polymerization of propylene in each stage in a continuous manner in order to produce the first polypropylene resin composition according to the present invention in an efficient and economical way, a continuous polymerization may often bring about occurrence of gel formation. In order to suppress gel formation as scarce as possible, it is favorable to carry out the production of the polypropylene product of relatively lower molecular weight in the second and the subsequent stages using at least two polymerization reactors, preferably at least three reactors in a continuous manner in each reactor and to perform transference of the polymerization product from a reactor to another reactor also in a continuous way. By performing the production of polypropylene products in the second and the subsequent stages continuously using a plurality of reactors, a polypropylene resin composition exhibiting scarce occurrence of gel formation can be obtained.
The Second Polypropylene Resin Composition
The second polypropylene resin composition according to the present invention comprises polypropylene as a main component and has, for the resin composition as a whole, the characteristic features 1), 2), 4), 5), 7) and 8) given below. The second polypropylene resin composition may either be constituted exclusively of polypropylene or contain other resin(s) than polypropylene in a small proportion.
1) A melt flow rate (MFR), determined according to ASTM D1238 at 230xc2x0 C. under a load of 2.16 kg, in the range of 0.01-20 g/10 min., preferably 0.05 -10 g/10 min.
2) A content of a high molecular weight part polypropylene having an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g, preferably of 8.5-12 dl/g, in the range of 20-50% by weight, preferably 25-45% by weight.
4) A molecular weight distribution, determined by gel permeation chromatography (GPC), in the range of 6-20, preferably 6-13 for Mw/Mn (weight-average molecular weight/number-average molecular weight) and 4 or higher, preferably in the range of 4-7 for Mz/Mw (z-average molecular weight/weight-average molecular weight).
5) An isotactic pentad fraction (mmmm fraction), determined by 13C-NMR, of at least 97%, preferably in the range of 98.0-99.5%.
7) A melt tension (MT), determined by flow tester at 230xc2x0 C., in the range of 5-30 g, preferably 8-30 g.
8) A relationship between the melt tension (MT), determined by flow tester at 230xc2x0 C., and the critical shearing rate (SRc) satisfying the following formula (I) or, preferably, following formula (Ixe2x80x2), namely,
MT greater than xe2x88x924.16xc3x97Ln(SRc)+29xe2x80x83xe2x80x83(I)
MT greater than xe2x88x924.16xc3x97Ln(SRc)+33xe2x80x83xe2x80x83(Ixe2x80x2)
xe2x80x83in which MT represents the melt tension in gram, SRc represents the critical shearing rate in secxe2x88x921 and Ln indicates the natural logarithm.
The isotactic pentad fraction (mmmm fraction) and the melt tension (MT) can be determined in the same method as described previously in the disclosure of the first polypropylene resin composition. The critical shearing rate (SRc) represents the shearing velocity at which melt fracture commences and can be determined using Flow Tester provided with an orifice having a diameter of 1 mm and a length of 10.9 mm by extruding the molten polypropylene resin composition through the orifice at a temperature of 230xc2x0 C. at an extrusion velocity of 0.5 mm/min. under successive increase of the extrusion velocity, in order to observe the extrusion velocity at which melt fracture of the extruded strand begins to occur.
The molecular weight distribution expressed by an Mw/Mn value of 6-20 and an Mz/Mw value of 4 or higher indicates that the molecular distribution of the second polypropylene resin composition according to the present invention is more widely shifted towards high molecular weight side as compared with ordinary polypropylene product.
For the second polypropylene resin composition according to the present invention, preference is given to those which have further, in addition to the characteristic features 1), 2), 4), 5), 7) and 8), the following characteristic feature 3):
3) A gel areal density, as determined by the method explained previously, in number of 3,000/450 cm2 or less, preferably 2,500/450 cm2 or less, more preferably 2,000/450 cm2 or less.
The second polypropylene resin composition according to the present invention has a high melt tension and is superior in the moldability and in the stiffness as well, since the molecular weight distribution is within the specific range as above and the melt tension is in a specific relation with the critical shearing rate.
The polypropylene product to be present as the main component of the second polypropylene resin composition according to the present invention may preferably be composed exclusively of the structural unit derived from propylene, though it may include other structural unit(s) derived from other comonomer(s) than propylene in a small proportion, such as 10 mole % or lower, preferably 5 mole % or lower. Such other comonomer may include, for example, xcex1-olefins other than propylene, such as ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene; vinyl compounds, such as styrene, vinylcyclopentene, vinylcyclohexane and vinylnorbornane; vinyl esters, such as vinyl acetate and the like; unsaturated organic acids and derivatives thereof, such as maleic anhydride and the like; conjugated diene compounds; non-conjugated polyenes, such as dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylenenorbornene and 5-ethylidene-2-norbornene. Among them, preference is given to ethylene and xcex1-olefins having 4-10 carbon atoms. They may be present as copolymers of two or more of them.
The second polypropylene resin component according to the present invention may contain, as a prepolymer, 0.1% by weight or less, preferably 0.05% by weight or less, of a homopolymer or copolymer of branched olefins, for example, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 3-methyl-1-hexene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 3,5,5-trimethyl-1-hexene, vinylcyclopentane, vinylcyclohexane, vinylcycloheptane, vinylnorbornane, allylnorbornane, styrene, dimethylstyrene, allylbenzene, allyltoluene, allylnaphthalene and vinylnaphthalene. Among them, special preference is given to 3-methyl-1-butene and the like.
The polypropylene constituting the second polypropylene resin composition according to the present invention may also be a block-copolymer of propylene, which is favorable due to a possible attainment of a superior impact resistance in addition to a superior stiffness, wherein special preference is given to a propylene/ethylene block-copolymer of which rubber part has an intrinsic viscosity [xcex7] of 0.5-10 dl/g.
For the polypropylene product constituting the second polypropylene resin composition according to the present invention, a polypropylene product exhibiting the characteristic features 1), 2), 4), 5), 7) and 8) or the characteristic features 1) to 5), 7) and 8) may be employed as such therefor, so long as it can be produced within a single stage polymerization, while the polypropylene product comprises polymers of widespread molecular weights from relatively lower ones to relatively higher ones. While it is permissible here to produce polypropylene products having different molecular weights separately and blend them by melt-mixing, it is preferable to produce polypropylene products having different molecular weights in a multi-stage polymerization of at least two stages to thereby obtain a product comprising polymers of wide variety of molecular weights of relatively lower to relatively higher ones. While it is permissible to produce the polypropylene products of relatively higher molecular weights and the polypropylene products of relatively lower molecular weights separately but not in a multistage polymerization and, then, to blend them together by melt mixing, this causes a tendency to gel-formation and is not favorable. For a favorable practice for producing the second polypropylene resin composition according to the present invention, there may be exemplified a process in which propylene is polymerized alone or together with other comonomer(s) in the presence of a catalyst for producing stereospecific polypropylene in a multistage polymerization of at least two stages.
As a concrete practice for realizing multistage polymerization, there may be exemplified a process of two-stage polymerization, which comprises
producing, in a first stage, 20-50%, preferably 25-45%, based on the weight of the finally obtained polypropylene resin composition as a whole, of a polypropylene product of relatively higher molecular weight having an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g, preferably 8.5-12 dl/g, and
producing, in a second stage, 50-80%, preferably 55-75%, based on the weight of the finally obtained polypropylene resin composition as a whole, of a polypropylene product of relatively lower molecular weight having an intrinsic viscosity [xcex7] (this intrinsic viscosity [xcex7] refers to the intrinsic viscosity [xcex7] of the polypropylene product produced in the second stage solely containing no polypropylene product produced in the first stage) of 0.8-4 dl/g.
There may also be exemplified alternatively a process of three-stage polymerization for producing the second polypropylene resin composition according to the present invention, which comprises
producing, in the first stage, 20-50%, preferably 25-45%, based on the weight of the finally obtained polypropylene resin composition as a whole, of a polypropylene product of relatively higher molecular weight having an intrinsic viscosity [xcex7], determined at 135xc2x0 C. in decalin, of 8-13 dl/g, preferably 8.5-12 dl/g, and
producing, in the second stage, a polypropylene product in such a manner that the intrinsic viscosity [xcex7] of the entire product as a whole (this intrinsic viscosity [xcex7] refers to the intrinsic viscosity [xcex7] of the entire polypropylene product containing the polypropylene product produced in the first stage) of 3-10 dl/g and
producing, in the third stage, a polypropylene product in such a manner that the intrinsic viscosity [xcex7] of the entire product as a whole (this intrinsic viscosity [xcex7] refers to the intrinsic viscosity [xcex7] of the entire polypropylene product containing the polypropylene products produced in the first and the second stages) of 0.8-6 dl/g.
In the above multistage polymerization, the first stage polymerization may preferably be performed under substantial absence of hydrogen. For the sequence of polymerization course, it is preferable to carry out the production of the polypropylene of relatively higher molecular weight in the first stage and to effect thereafter production of the polypropylene product(s) of relatively lower molecular weight in the subsequent stage(s). While the production sequence may be reversed, it should be necessary therefor to incorporate exhaustive elimination of the molecular weight regulator, such as hydrogen, included in the first stage reaction product before the initiation of polymerization in the second or subsequent stage(s), in order to produce a polypropylene product of relatively lower molecular weight in the first stage and to produce a polypropylene product of relatively higher molecular weight in the second and the subsequent stages, so that employment of an intricated apparatus becomes necessary and attainment of increase in the intrinsic viscosity [xcex7] of the polypropylene product in the second and the subsequent stages may not be easy.
The polymerization in each stage may be realized either continuously or in a batchwise process. The polymerization may be performed in a known practice, for example, by slurry polymerization or by bulk polymerization. The polymerization in the second and the subsequent stages may preferably be carried out subsequently to the first stage polymerization in a continuous manner. When a batch process is employed, the multistage polymerization can be effected in one single reactor.
While it is favorable to carry out the polymerization of propylene in each stage in a continuous manner in order to produce the first polypropylene resin composition according to the present invention in an efficient and economical way, a continuous polymerization may often bring about occurrence of gel formation. In order to suppress gel formation as scarce as possible, it is favorable to carry out the production of the polypropylene product of relatively lower molecular weight in the second and the subsequent stages using at leat two polymerization reactors, preferably at least three reactors, in a continuous manner in each reactor and to perform transference of the polymerization product from a reactor to another reactor also in a continuous way. By performing the production of polypropylene products continuously using a plurality of reactors, a polypropylene resin composition exhibiting scarce occurrence of gel formation can be obtained.
For the catalyst for producing the highly stereospecific polypropylene to be used in the production of the first and the second polypropylene resin compositions according to the present invention, there may be employed various known catalysts, for example, a catalyst composed of
(a) a solid catalyst component based on titanium, which has contents of magnesium, titanium, halogen and an electron donating agent,
(b) an organometallic compound catalyst component
(c) an organosilicic compound catalyst component having at least one substituent selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and their derivatives.
The solid catalyst based on titanium (a) mentioned above can be prepared by bringing a magnesium compound (a-1), a titanium compound (a-2) and an electron donor (a-3) into contact with each other.
As the magnesium compound (a-1), there may be enumerated magnesium compounds having reducing ability, such as compounds having carbon-to-magnesium bond or magnesium-to-hydrogen bond, and magnesium compounds having no reducing ability, such as those represented by magnesium halogenides, alkoxymagnesium halides, aryloxymagnesium halides, alkoxymagnesiums, aryloxymagnesiums and carboxylic acid salts of magnesium.
In preparing the titanium-based solid catalyst component (a), it is preferable that, for example, a tetravalent titanium compound represented by the formula (1) given below is employed as the titanium compound (a-2).
Ti(OR)gX4xe2x88x92gxe2x80x83xe2x80x83(1)
In the formula (1), R represents a hydrocarbon group, X denotes a halogen atom and g is in the range of 0xe2x89xa6gxe2x89xa64.
Concrete examples of the above titanium compound represented by the formula (1) include titanium tetrahalides, such as TiCl4, TiBr4 and TiI4; alkoxytitanium trihalides, such as Ti(OCH3)Cl3, Ti(OC2H5)Cl3, Ti(O-n-C4H9)Cl3, Ti(OC2H5)Br3, and Ti(O-iso-C4H9)Br3; dialkoxytitanium dihalides, such as Ti(OCH3)2Cl2, Ti(OC2H5)2Cl2, Ti(O-n-C4H9)2Cl2 and Ti(OC2H5)2Br2; trialkoxytitanium monohalides, such as Ti(OCH3)3Cl, Ti(OC2H5)3Cl, Ti(O-n-C4H9)3Cl and Ti(OC2H5)3Br; and tetraalkoxytitanium, such as Ti(OCH3)4, Ti(OC2H5)4, Ti(O-n-C4H9)4, Ti(O-iso-C4H9)4 and Ti(O-2-ethylhexyl)4.
For the electron donor (a-3) to be incorporated in the preparation of the titanium-based solid catalyst component (a), there may be exemplified alcohols, phenols, ketones, aldehydes, esters of organic or inorganic acids, organic acid halides, ethers, acid amides, acid anhydrides, ammonia, amines, nitriles, isocyanates, nitrogen-containing cyclic compounds and oxygen-containing cyclic compounds.
In contacting the magnesium compound (a-1), the titanium compound (a-2) and the electron donor (a-3) with each other, it is permissible that other reaction reagent, such as silicium, phosphorus or aluminum, may be caused to be present simultaneously and it is also permissible to incorporate a solid catalyst carrier for preparing a carrier-supported solid titanium catalyst component (a).
The titanium-based solid catalyst component (a) may be prepared by any technique including known one. Examples of such preparation technique are given below in a brief description:
(1) A technique in which a solution of the magnesium compound (a-1) in a hydrocarbon solvent containing the electron donor (the liquefying agent) (a-3) is brought into contact with the organometallic compound to cause a reaction to presipitate solid matter which is then, or in the course of precipitation, brought into contact with the titanium compound (a-2) to cause reaction.
(2) A technique in which a complex composed of the magnesium compound (a-1) and the electron donor (a-3) is brought into contact with the organometallic compound to cause reaction and, then, the titanium compound (a-2) is caused to contact and react therewith.
(3) A technique in which the contacted product from the contact of an inorganic carrier with an organomagnesium compound (a-1) is brought into contact with the titanium compound (a-2) and with the electron donor (a-3) to cause reaction therebetween. Here, it is permissible to bring the product of contact of the carrier with the magnesium compound into contact with a halogen-containing compound and/or an organometallic compound preliminarily.
(4) A technique, wherein a solid carrier, which is obtained from a mixture containing a solution of the magnesium compound (a-1), the electron donor (a-3) and the carrier in a liquid medium of the liquefying agent and, optionally, a hydrocarbon solvent and on which the magnesium compound (a-1) is supported, is contacted with the titanium compound (a-2).
(5) A technique in which a solution containing the magnesium compound (a-1), the titanium compound (a-2), the electron donor (a-3) and, optionally, a hydrocarbon solvent is brought into contact with a solid carrier.
(6) A technique in which an organomagnesium compound (a-1) in liquid form and a halogen-containing titanium compound (a-2) are brought into contact with each other. In this case, the electron donor (a-3) is used at least once.
(7) A technique in which an organomagnesium compound (a-1) in liquid form and a halogen-containing titanium compound (a-2) are brought into contact with each other, whereupon the resulting product is caused to contact with the titanium compound (a-2). In this case, the electron donor (a-3) is used at least once.
(8) A technique in which an alkoxyl group-containing magnesium compound (a-1) is brought into contact with a halogen-containing titanium compound (a-2). In this case, the electron donor (a-3) is used at least once.
(9) A technique in which a complex composed of an alkoxyl group-containing magnesium compound (a-1) and of the electron donor (a-3) is brought into contact with the titanium compound (a-2).
(10) A technique in which a complex composed of an alkoxyl group-containing magnesium compound (a-1) and the electron donor (a-3) is brought into contact with an organometallic compound, whereupon the resulting product is brought into contact with the titanium compound (a-2).
(11) A technique in which the magnesium compound (a-1), the electron donor (a-3) and the titanium compound (a-2) are brought into contact with each other in a voluntary order to cause reactions therebetween. It is permissible to incorporate a pretreatment of each reaction component before these reactions using a reaction assistant, such as an electron donor (a-3), an organometallic compound, a halogen-containing silicium compound or the like.
(12) A technique in which a liquid magnesium compound (a-1) exhibiting no reducing function is caused to react with a liquid titanium compound (a-2) in the presence of the electron donor (a-3) to deposit a solid magnesium/titanium composite product.
(13) A technique in which the reaction product obtained in the above (12) is further reacted with the titanium compound (a-2).
(14) A technique in which the reaction product obtained in the above (11) or (12) is further reacted with the electron donor (a-3) and with the titanium compound (a-2).
(15) A technique in which a solid mixture obtained by crushing the magnesium compound (a-1), the titanium compound (a-2) and the electron donor (a-3) is treated with either an elementary halogen, a halogen compound or an aromatic hydrocarbon. In this case, it is permissible to incorporate a process step of crushing either the magnesium compound (a-1) solely, a complex composed of the magnesium compound (a-1) and of the electron donor (a-3) or the magnesium compound (a-1) and the titanium compound (a-2). It is also permissible to subject the crushed product to a pretreatment with a reaction assistant, followed by an after-treatment with, such as, an elementary halogen. As the reaction assistant, for example, an organometallic compound or a halogen-containing silicium compound, may be employed.
(16) A technique in which the magnesium compound (a-1) is crushed and the resulting crushed product is brought into contact with the titanium compound (a-2). Upon crushing and/or contacting the magnesium compound (a-1), an electron donor (a-3) may, if necessary, be employed together with a reaction assistant.
(17) A technique in which the product obtained in either of the above (11)-(16) is treated with an elementary halogen or a halogen compound or with an aromatic hydrocarbon.
(18) A technique in which a reaction product resulting after the metal oxide, the organomagnesium compound (a-1) and the halogen-containing compound are contacted with each other is caused to contact with the electron donor (a-3) and with, preferably, the titanium compound (a-2).
(19) A technique in which a magnesium compound (a-1), such as a magnesium salt of an organic acid, an alkoxymagnesium or an aryloxymagnesium, is brought into contact with the titanium compound (a-2), with the electron donor (a-3) and, if necessary, further with a halogen-containing hydrocarbon.
(20) A technique in which a solution of the magnesium compound (a-1) and an alkoxytitanium in a hydrocarbon solvent is brought into contact with the electron donor (a-3) and, if necessary, further with the titanium compound (a-2). In this case, it is favorable that a halogen-containing compound, such as a halogen-containing silicium compound, is caused to co-exist.
(21) A technique in which a liquid magnesium compound (a-1) exhibiting no reducing function is caused to react with an organometallic compound to cause a composite solid product of magnesium/metal (aluminum) to deposit out and, then, the product is reacted with the electron donor (a-3) and with the titanium compound (a-2).
As the organometallic compound catalyst component (b) mentioned above, those which contain a metal selected among the Group I to Group III of the periodic table are preferred. Concretely, there may be exemplified organoaluminum compounds, complex alkyl compounds with Group I metal and aluminum, organometallic compounds of Group II metals and so on, represented by the formulae given below:
An organoaluminum compound (b-1) represented by the formula
R1mAl(OR2)nHpXq
In which R1 and R2 represent each a hydrocarbon group having usually 1-15 carbon atoms, preferably 1-4 carbon atoms, which may be identical with or different from each other, X denotes a halogen atom, m is in the range 0 less than mxe2x89xa63, n is in the range 0xe2x89xa6n less than 3, p is in the range 0xe2x89xa6p less than 3 and q is in the range 0xe2x89xa6q less than 3, wherein m+n+p+q=3.
An alkylated complex of a Group I metal and aluminum (b-2) represented by the formula
M1AlR14
In the formula, M1 is Li, Na or K and R1 has the same meaning as above.
A dialkylated compound of Group II or Group III metal (b-3) represented by the formula
R1R2M2
In the formula, R1 and R2 have the same meanings as above and M2 is Mg, Zn or Cd.
As the organoaluminum compound (b-1), there may be enumerated, for example, those which are represented by the formula
R1mAl(OR2)3xe2x88x92m,
in which R1 and R2 have the same meanings as above and m is preferably of 1.5xe2x89xa6mxe2x89xa63; those which are represented by the formula
R1mAlX(3xe2x88x92m),
in which R1 has the same meaning as above, X stands for a halogen and m is preferably of 0 less than m less than 3; those which are represented by the formula
R1mAlH(3xe2x88x92m),
in which R1 has the same meaning as above and m is preferably of 2xe2x89xa6m less than 3; and those which are represented by the formula
R1mAl(OR2)nXq,
in which R1 and R2 have the same meanings as above, X stands for a halogen, m is in the range 0 less than mxe2x89xa63, n is in the range 0xe2x89xa6n less than 3 and q is in the range 0xe2x89xa6q less than 3, wherein m+n+q=3.
Concrete examples of the organosilicic compound catalyst component (c) include organosilicic compounds represented by the formula (2) given below
SiR1R2n(OR3 )(3xe2x88x92n)xe2x80x83xe2x80x83(2)
In the formula (2), n is an integer of 0, 1 or 2, R1 is a radical selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and their derivatives and R2 and R3 denote each a hydrocarbyl radical.
As the concrete examples of R1 in the formula (2), there may be enumerated cyclopentyl and derivatives thereof, such as cyclopentyl, 2-methylcyclopentyl, 3-methylcyclopentyl, 2-ethylcyclopentyl, 3-propylcyclopentyl, 3-isopropylcyclopentyl, 3-butylcyclopentyl, 3-tert-butylcyclopentyl, 2,2-dimethylcyclopentyl, 2,3-dimethylcyclopentyl, 2,5-dimethylcyclopentyl, 2,2,5-trimethylcyclopentyl, 2,3,4,5-tetramethylcyclopentyl, 2,2,5,5-tetramethylcyclopentyl, 1-cyclopentylpropyl and 1-methyl-1-cyclopentylethyl; cyclopentenyl and derivatives thereof, such as cyclopentenyl, 2-cyclopentenyl, 3-cyclopentenyl, 2-methyl-1-cyclopentenyl, 2-methyl-3-cyclopentenyl, 3-methyl-3-cyclopentenyl, 2-ethyl-3-cyclopentenyl, 2,2-dimethyl-3-cyclopentenyl, 2,5-di-methyl-3-cyclopentenyl, 2,3,4,5-tetramethyl-3-cyclopentenyl and 2,2,5,5-tetramethyl-3-cyclopentenyl; cyclopentadienyl and derivatives thereof, such as 1,3-cyclopentadienyl, 2,4-cyclopentadienyl, 1,4-cyclopentadienyl, 2-methyl-1,3-cyclopentadienyl, 2-methyl-2,4-cyclopentadienyl, 3-methyl-2,4-cyclopentadienyl, 2-ethyl-2,4-cyclopentadienyl, 2,2-dimethyl-2,4-cyclopentadienyl, 2,3-dimethyl-2,4-cyclopentadienyl, 2,5-dimethyl-2,4-cyclopentadienyl and 2,3,4,5-tetramethyl-2,4-cyclopentadienyl; derivatives of cyclopentyl, of cyclopentenyl and of cyclopentadienyl, such as indenyl, 2-methylindenyl, 2-ethylindenyl, 2-indenyl, 1-methyl-2-indenyl, 1,3-dimethyl-2-indenyl, indanyl, 2-methylindanyl, 2-indanyl, 1,3-dimethyl-2-indanyl, 4,5,6,7-tetrahydroindenyl, 4,5,6,7-tetrahydro-2-indenyl, 4,5,6,7-tetrahydro-1-methyl-2-indenyl, 4,5,6,7-tetrahydro-1,3-dimethyl-2-indenyl and fluorenyl.
Concrete examples of the hydrocarbyl groups R2 and R3 in the formula (2) include alkyls, cycloalkyls, aryls and aralkyls. If two or more groups are present for R2 or/and R3, the groups of R2, or/and of R3 may either be identical with or different from each other, wherein R2 may either be identical with or different from R3. The groups R1 and R2 in the formula (2) may be coupled with each other via a bridging group, such as alkylene.
Among the organosilicic compounds represented by the formula (2), preference is given to those in which R1 stands for cyclopentyl, R2 represents an alkyl or cyclopentyl and R3 stands for an alkyl, especially methyl or ethyl.
Concrete examples of the organosilicic compounds represented by the formula (2) include trialkoxysilanes, such as cyclopentyltrimethoxysilane, 2-methylcyclopentyltrimethoxysilane, 2,3-dimethylcyclopentyltrimethoxysilane, 2,5-dimethylcyclopentyltrimethoxysilane, cyclopentyltriethoxysilane, cyclopentenyltrimethoxysilane, 3-cyclopentenyltrimethoxysilane, 2,4-cyclopentadienyltrimethoxysilane, indenyltrimethoxysilane, and fluorenyltrimethoxysilane; dialkoxysilanes, such as dicyclopentyldimethoxysilane, bis(2-methylcyclopentyl)dimethoxysilane, bis(3-tert-butylcyclopentyl)dimethoxysilane, bis(2,3-dimethylcyclopentyl)dimethoxysilane, bis(2,5-dimethylcyclopentyl)dimethoxysilane, dicyclopentyldiethoxysilane, dicyclopentenyldimethoxysilane, di(3-cyclopentenyl)dimethoxysilane, bis(2,5-dimethyl-3-cyclopentenyl)dimethoxysilane, di-2,4-cyclopentadienyldimethoxysilane, bis(2,5-dimethyl-2,4-cyclopentadienyl)dimethoxysilane, bis(1-methyl-1-cyclopentylethyl)dimethoxysilane, cyclopentylcyclopentenyldimethoxysilane, cyclopentylcyclopentadienyldimethoxysilane, diindenyldimethoxysilane, bis(1,3-dimethyl-2-indenyl)dimethoxysilane, cyclopentadienylindenyldimethoxysilane, difluorenyldimethoxysilane, cyclopentylfluorenyldimethoxysilane and indenylfluorenyldimethoxysilane; monoalkoxysilanes, such as tricyclopentylmethoxysilane, tricyclopentenylmethoxysilane, tricyclopentadienylmethoxysilane, tricyclopentylethoxysilane, dicyclopentylmethylmethoxysilane, dicyclopentylethylmethoxysilane, dicyclopentylmethylethoxysilane, cyclopentyldimethylmethoxysilane, cyclopentyldiethylmethoxysilane, cyclopentyldimethylethoxysilane, bis(2,5-dimethylcyclopentyl)cyclopentylmethoxysilane, dicyclopentylcyclopentenylmethoxysilane, dicyclopentylcyclopentadienylmethoxysilane and diindenylcyclopentylmethoxysilane; and others, such as ethylenebiscyclopentyldimethoxysilane.
For polymerizing propylene using a catalyst composed of the solid titanium catalyst component (a), the organometallic compound catalyst component (b) and the organosilicic compound catalyst (c), a prepolymerization may be incorporated. In the prepolymerization, an olefin is polymerized in the presence of a solid titanium catalyst component (a), an organometallic compound catalyst component (b) and, if necessary, an organosilicic compound catalyst component (c).
For the olefin to be pre-polymerized, there may be used, for example, a linear olefin, such as ethylene, propylene, 1-butene, 1-octene, 1-hexadecene or 1-eicosene; or an olefin having branched structure, such as 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1- hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, allylnaphthalene, allylnorbornane, styrene, dimethylstyrenes, vinylnaphthalenes, allyltoluenes, allylbenzene, vinylcyclohexane, vinylcyclopentane, vinylcycloheptane or allyltrialkylsilanes. They may be co-polymerized.
The prepolymerization may favorably be carried out in such a manner that the polymerized product will be formed in an amount of about 0.1-1,000 g, preferably 0.3-500 g per one gram of the solid titanium catalyst component (a). If the pre-polymerized amount is too large, the efficiency for producing the (co)polymer in the inherent polymerization may decrease. In the prepolymerization, the catalyst may be used at a concentration considerably higher than that in the system of the inherent polymerization.
Upon the multistage polymerization of propylene using the catalyst as above, it is permissible to subject propylene to a copolymerization with other comonomer(s) mentioned above in either one stage or in all the stages, so long as the purpose of the present invention is not obstructed.
In the multistage polymerization, propylene is subjected to homo-polymerization or to copolymerization with other comonomer(s) in each stage to produce a polypropylene product, wherein the polypropylene product may preferably have a content of the structural unit of propylene exceeding 90 mole %, preferably in the range of 95-100 mole %. The content of the structural unit of propylene in each stage can be adjusted by, for example, altering the amount of hydrogen supplied to each polymerization system. However, it is preferable to effect the polymerization in the first stage without supplying hydrogen thereto, when a high molecular weight polypropylene is to be produced there.
On the multistage polymerization of propylene, it is permissible to incorporate in the polymerization process a stage of copolymerization of propylene with ethylene in addition to the prulality of polymerization stages mentioned above, in order to form a propylene/ethylene copolymer rubber to produce a propylene block-copolymer.
For the intrinsic polymerization, it is favorable to use the solid titanium catalyst component (a) (or the catalyst for the prepolymerization) in an amount of about 0.0001-50 mmol, preferably about 0.001-10 mmol, calculated as titanium atom, per one liter of the polymerization volume. The organometallic compound catalyst component (b) may favorably be used in an amount of about 1-2,000 moles, preferably about 2-500 moles, as calculated for the atomic weight of the metal per one mole of titanium atom in the polymerization system. The organosilicic compound catalyst component (c) may favorably be used in an amount of about 0.001-50 moles, preferably about 0.01-20 moles, per one mole of the metal atom of the organometallic compound catalyst component (b).
The polymerization may be effected in either of gas phase polymerization or liquid phase polymerization such as solution polymerization and suspension polymerization, wherein each stage may be realized in a different way. It may be performed either in a batchwise, continuous or semi-continuous way. Each of the stages may be performed in a plurality of polymerization reactors, for example, in 2-10 reactors. For industrial production, it is most preferably to carry out the polymerization in continuous way, wherein preference is given to such a practice that the polymerization in the second or the subsequent stage is effected in at least two separate polymerization reactors, whereby gel-formation can be suppressed.
As the polymerization medium, inert hydrocarbon may be used and propylene in liquid state may be used therefor. The polymerization condition may be selected adequately within the ranges for the polymerization temperature of about xe2x88x9250xc2x0 C. to +200xc2x0 C., preferably about 20xc2x0 C. to 100xc2x0 C., and for the polymerization pressure of normal pressure to 9.8 MPa (normal pressure to 100 kgf/cm2 gauge), preferably about 0.2 to 4.9 MPa (about 2 to 50 kgf/cm2 gauge).
The first polypropylene resin composition and the second polypropylene resin composition according to the present invention can be used after blending them. It is permissible that each of the first and the second polypropylene resin compositions according to the present invention contains on requirement other polymer(s) and/or additives etc., so long as the purpose of the present invention is not obstructed. As the said other polymers, polypropylenes which are not included in the first and the second polypropylene resin compositions according to the present invention, for example, homopolymer of propylene and propylene/xcex1-olefin copolymers, are enumerated. As others, there may be enumerated, for example, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polyolefins, rubber components and engineering plastics. For example, the first or the second polypropylene resin composition according to the present invention may contain, for improving the impact strength, a rubber component, such as an ethylene/xcex1-olefin copolymer rubber or a rubber based on a conjugated diene, in an adequate amount. Concrete examples of such a rubber component include non-crystalline or low-crystalline xcex1-olefin copolymers having no diene component, such as ethylene/propylene copolymer rubber, ethylene/1-butene copolymer rubber, ethylene/1-octene copolymer rubber and propylene/ethylene copolymer rubber; ethylene/propylene/dicyclopentadiene copolymer rubber; ethylene/propylene/non-conjugated diene copolymer rubber, such as ethylene/propylene/1,4-hexadiene copolymer rubber, ethylene/propylene/cyclooctadiene copolymer rubber, ethylene/propylene/methylenenorbornene copolymer rubber and ethylene/propylene/ethylidenenorbornene copolymer rubber; and ethylene/butadiene copolymer rubber.
As the additives, there may be enumerated, for example, nucleating agent, antioxidant, hydrochloric acid absorber, heat stabilizer, anti-weathering agent, light stabilizer, UV-absorber, slipping agent, anti-blocking agent, antifogging agent, lubricating agent, antistatic agent, flame retardant, pigments, colorants, dispersant, copper-sequestering agent, neutralizing agent, foaming agent, plasticizer, bubble preventing agent, cross-linking agent, flowability improving agent such as peroxides, weld strength improving agent, natural petroleum oils, synthetic oils, waxes and inorganic fillers such as talc etc.
The first and the second polypropylene resin compositions according to the present invention may contain the above-mentioned prepolymer, as a nucleating agent, or an inherent nucleating agent chosen among known ones or, further, the above-mentioned prepolymer together with an inherent nucleating agent. By inclusion or addition of a nucleating agent, micronization of the crystal grains and increment of the crystallization velocity are attained, whereby a high speed molding can be realized. For example, when a nucleating agent is contained in the first and the second polypropylene resin compositions according to the present invention, it is possible to provide for a micronization of the crystals together with attainment of increased crystallization velocity to permit high speed molding. For the nucleating agent other than the prepolymer mentioned above, various nucleating agent known previously, such as nucleating agents based on phosphate, sorbitol, metal salts of aromatic or aliphatic carboxylic acids and inorganic substances, may be employed without any restriction.
The first and the second polypropylene resin compositions according to the present invention have a high melt tension (MT) and are superior in the moldability and in the stiffness, so that they can be processed into molded articles of not only small sizes but also large sizes, which have better appearance and are difficultly deformable. Therefore, the first and the second polypropylene resin compositions according to the present invention can be used without any limitation for various application fields where the above-mentioned characteristic properties are required. Thus, they are adapted for use as the starting material of, for example, blow-molded articles, vacuum-formed articles, pressure-formed articles, calendered articles, stretched films, inflation films, extrusion molded articles and foamed articles, while they can be used as the starting material for other molded articles and for other molding techniques.
The resin composition for blow molding according to the present invention is constituted of a resin blend comprising the first and/or the second polypropylene resin composition, other resins including one or more ethylenic polymers including a low density polyethylene (LDPE) and a high density polyethylene (HDPE), an ethylene/xcex1-olefin random copolymer and elastomer(s) based on styrene, fillers and additives. The proportion of the summed-up amount of the first and the second polypropylene resin compositions according to the present invention in the resin composition for blow molding may favorably be in the range of 50-99% by weight, preferably 50-90% by weight. The resin composition for blow molding according to the present invention per se has also a high melt tension (MT) and is superior in the moldability and in the stiffness, so that it can be used favorably as the material to be processed by blow molding, in particular for large-sized articles, such as for example, those in which the weight of the parison is 5 kg or higher.
The blow-molded article according to the present invention is a hollow product prepared by subjecting the first or the second polypropylene resin composition according to the present invention, or the resin composition for blow molding according to the present invention, to a blow molding. For blow molding the first polypropylene resin composition according to the present invention, it is preferable that the first polypropylene resin composition has the following characteristic feature 8), namely,
8) that the relationship between the melt tension (MT), determined by Flow Tester at 230xc2x0 C., and the critical shearing rate (SRc) meets the following formula (I), preferably the following formula (Ixe2x80x2):
MT greater than xe2x88x924.16xc3x97Ln(SRc)+29xe2x80x83xe2x80x83(I)
MT greater than xe2x88x924.16xc3x97Ln(SRc)+33xe2x80x83xe2x80x83(Ixe2x80x2)
in which MT represents the melt tension in gram. SRc represents the critical shearing rate in secxe2x88x921 and Ln indicates the natural logarithm.
The blow-molded article according to the present invention is produced from the polypropylene resin composition according to the present invention having a high melt tension, so that the parison will scarcely suffer from occurrence of draw-down and from occurrence of waving and rough surface even in a large-sized parison. Therefore, blow-molded articles of not only small size but also large size can be obtained easily with better appearance in an efficient manner. For example, a large-sized blow-molded article, such as bumper or spoiler of automobile produced from a parison having a weight of 5 kg or more, can be produced at a high speed efficiently. Due to the superior stiffness, the resulting blow-molded articles are scarcely deformable.
For producing the blow-molded article according to the present invention from the above-mentioned polypropylene resin composition, known blow molding apparatuses can be employed. The molding conditions may also be those known ones.
In the case of extrusion blow molding, a blow-molded article can be obtained by extruding the polypropylene resin composition according to the present invention in a molten state at a resin temperature of, for example, 170 to 300xc2x0 C., preferably 170 to 270xc2x0 C., through a die to form a tubular parison and placing this parison in a mold having the shape corresponding to that of the molded article, whereupon air is blown into this parison at a resin temperature of 130 to 300xc2x0 C., preferably 200 to 270xc2x0 C., in order to fit it to the mold inner face to obtain the contemplated blow-molded article. The extension magnification may preferably be 1.5- to 5-fold in the lateral direction.
In the case of injection blow molding, the polypropylene resin composition according to the present invention is injected into a mold at a resin temperature of, for example, 170 to 300xc2x0 C., preferably 170 to 270xc2x0 C., to form a parison, whereupon the parison is placed in a mold of a shape corresponding to that of the molded article and air is blown into the parison in order to fit it to the mold at a resin temperature of 120 to 300xc2x0 C., preferably 140 to 270xc2x0 C., to obtain the blow-molded article. The extension magnification may preferably be 1.1- to 1.8-fold in the longitudinal direction and 1.3- to 2.5-fold in the lateral direction.
In the case of stretching blow molding, the polypropylene resin composition according to the present invention is injected into a mold at a resin temperature of, for example, 170 to 300xc2x0 C., preferably 170 to 280xc2x0 C., to form a parison which is then preliminarily blown under a predetermined condition, whereupon this pre-blown parison is subjected to a stretching blow molding at a resin temperature of 80 to 200xc2x0 C., preferably 100 to 180xc2x0 C., to obtain the blow-molded article. The extension magnification may preferably be 1.2- to 4.5-fold in the longitudinal direction and 1.2- to 8-fold in the lateral direction.
Concrete examples of the blow-molded article according to the present invention include automobile exterior furnishings, such as spoiler, bumper, side molding, front grill guard and bumper guard; automobile interior furnishings, such as sun visor, radiator tank, washer tank, ducts, distributor, evaporator casing, console box, indicator panel and door trim; vessels, such as kerosene tank, vessels for foods, shampoo cartridge, containers for cosmetics, containers for detergents, vessels for drugs and containers for toner; and others, such as toys and containers. Among them, large-sized blow-molded articles with parison weights of 5 kg and higher, in particular, automobile exterior furnishings, such as bumper and spoiler, may favorably be enumerated.
The vacuum- or pressure-formed article according to the present invention is produced by processing a sheet or film made of the first or the second polypropylene resin composition according to the present invention by vacuum- or pressure forming. Due to the high melt tension of the starting polypropylene resin composition, the sheet or film can sufficiently fit the shape of the mold inner face upon the vacuum- or pressure forming. Therefore, it can be processed by vacuum- or pressure forming at higher speed even in a large-sized article and permits deep drawing while providing superior strength and better appearance.
For producing the vacuum- or pressure-formed article according to the present invention from the polypropylene resin composition according to the present invention, known apparatuses for vacuum-forming or for pressure forming can be used. The forming conditions may also be those known ones. Thus, for example, a formed article in a form of sheet made of the polypropylene resin composition according to the present invention is held on a mold having a shape corresponding to that to be assumed at a temperature of 180-300xc2x0 C., preferably 180-270xc2x0 C., more preferably 180-250xc2x0 C., and, then, by evacuating the mold or by introducing a compressed air into the mold cavity, contemplated vacuum- or pressure-formed article can be obtained.
Concrete examples of the vacuum- or pressure-formed article according to the present invention include automobile interior furnishings, such as roof liner, refrigerator interior articles, laundry machine interior and exterior parts, jerry packages, instant lunch package, trays, trays for foods, foamed trays for foods, package for bean curd, cups, bags, heat resistant trays for electronic oven, protecting cases for machines and packaging cases for merchandizes.
The calendered article according to the present invention is produced by calendering the first or the second polypropylene resin composition according to the present invention. Due to the high melt tension of the starting polypropylene resin composition according to the present invention, sheet or film superior in the strength and gloss exhibiting scarce irregularity of thickness can easily be calendered at high speed.
For producing the calendered article according to the present invention from the polypropylene resin composition, known calendering apparatuses can be employed. The calendering conditions may also be known ones. For example, using a calendering machine of, for example, the series type, L-shaped type, reverse L-shaped type or Z-shaped type, calendering can be effected at a resin temperature of 180-300xc2x0 C., preferably 180-270xc2x0 C., and at a heating roll temperature of 170-300xc2x0 C., preferably 170-270xc2x0 C. It is also possible to produce an artificial leather, waterproof cloth or various laminates by feeding paper or cloth to the roll upon calendering.
Concrete examples of the calendered article according to the present invention include original sheets for processing into various cards and original sheets for producing household commodities.
The extrusion molded article according to the present invention is produced by extrusion-molding the first or the second polypropylene resin composition according to the present invention. Due to the high melt tension of the starting polypropylene resin composition according to the present invention, it can be subjected to extrusion molding at high speed and can be processed into a large-sized article having a high strength. In the case where the extrusion-molded article according to the present invention is an extruded sheet, the thickness thereof may range usually from 0.3 to 5 mm, preferably from 0.5 to 3 mm.
For producing the extrusion-molded article according to the present invention from the polypropylene resin composition according to the present invention, known extrusion apparatuses can be employed. For example, an extruding machine, such as monoaxial screw extruder, kneader extruder, ram extruder or gear extruder, can be used to produce an extruded sheet. The extruder may be provided with a circular die or a T-die. The conditions of extrusion may also be known ones, while it is preferable to effect the extrusion under the condition such as given below. For example, using an extruder provided with a T-die, a sheet may preferably be extruded at a resin temperature of 180-300xc2x0 C., preferably 180-270xc2x0 C., and at a T-die temperature of 180-300xc2x0 C., preferably 180-290xc2x0 C. For cooling the extruded article, water can be used, while other means, such as air-knife or cooling roll, may also be employed. It is also possible to produce an artificial leather, waterproof cloth or various laminates by feeding paper or cloth to the roll upon the extrusion.
Concrete examples of the extrusion-molded article according to the present invention include architectural furnishings, such as eaves gutter, curtain rail, window frame, shelves and door; extruded profile articles, such as cable ducts, roller shutters and shutters; and others, such as tubes, pipes, electric cables (sheathed), films, sheets, boards, fiber and tape.
The stretched film according to the present invention is a monoaxially or biaxially stretched film produced by stretching a sheet or film made of the first or the second polypropylene resin composition according to the present invention. Due to the high melt tension of the starting polypropylene resin composition according to the present invention, the resulting stretched film is superior in the thickness accuracy and can be produced at high speed stably without suffering from breaking of the film during the stretching. The stretched film according to the present invention has a thickness of, usually, 5-200 xcexcm, preferably 10-120 xcexcm. The stretching magnification ratio of the stretched film according to the present invention for biaxially stretched film is in the range of, usually, 9- to 100-fold, preferably 40- to 70-fold, and that for monoaxially stretched film in the range of, usually, 2- to 10-fold, preferable 2- to 6-fold.
For producing the stretched film according to the present invention from the polypropylene resin composition according to the present invention, known stretching apparatuses can be employed. For example, a tenter (with axial/lateral stretching or lateral/axial stretching), a simultaneous biaxial stretching machine or a monoaxial stretching machine may be exemplified. The conditions of stretching may also be known ones. For example, by melt-extruding the polypropylene resin composition according to the present invention at a temperature of 200-280xc2x0 C., preferably 240-270xc2x0 C., and stretching the resulting film up to 2- to 10-fold, preferably 2- to 6-fold in axial direction, a monoaxially stretched film can be produced. In an alternative technique, a biaxially stretched film can be obtained by melt-extruding the polypropylene resin composition according to the present invention at a temperature of 200-280xc2x0 C., preferably 240-270xc2x0 C., and stretching the resulting film under an atmosphere of 120-200xc2x0 C., preferably 130-180xc2x0 C., up to 3- to 10-fold in axial direction and up to 3- to 10-fold in lateral direction.
Concrete examples of the stretched film according to the present invention include packaging films for foods, such as candy and vegetable; shrinkable films for wrapping cup-noodle etc.; packaging film for packaging textile goods, such as utility shirt, T-shirt and panty stocking; films for office supplies, such as clear file, clear sheet; and others, such as capacitor film, cigarette packaging film, film for instant packaging, decoration film and packaging tape.
The inflation film according to the present invention is produced by subjecting the first or the second polypropylene resin composition according to the present invention to an inflation molding. Due to the high melt tension of the starting polypropylene resin composition according to the present invention, the balloon formed upon the inflation molding is held stable. Therefore, the inflation film according to the present invention exhibits scarce decrease in the strength and in the transparency and is superior in the stiffness and in the transparency, while permitting a high-speed molding, as seen in the film made of a resin blended with a high-pressure low density polyethylene.
For producing the inflation film according to the present invention from the polypropylene resin composition, known inflation-molding apparatuses can be employed. The conditions for the molding may also be those known ones. For example, a condition of a resin temperature of 180-240xc2x0 C., an air cooling in one or two stages at an air temperature of 10-40xc2x0 C., a rolling-up velocity of 5-200 m/min. and an inflation ratio of 1.1- to 5-fold may be employed. The inflation film may have a thickness in the range of 10 xcexcm to 1 mm, preferably 15 xcexcm to 0.5 mm.
Concrete examples of the inflation film according to the present invention include packaging films for foods, such as candy and vegetable; packaging film for packaging textile goods, such as utility shirt, T-shirt and panty stocking; films for office supplies, such as clear file, clear sheet; and others, such as cleaning bag, films for fashion bags, films for agricultural uses and cup.
The foamed article according to the present invention is produced by causing the first or the second popypropylene resin composition according to the present invention to foam up. To the technique for effecting the foaming, no special limitation is imposed and known techniques, such as foaming under normal pressure, extrusion foaming, pressure foaming, injection foaming and beads forming, can be employed. Due to the high melt tension of the starting polypropylene resin composition according to the present invention, foaming can be effected at a high foaming-up ratio in a uniform cell texture even for a large-sized foamed article. The foamed article according to the present invention can be produced by heating a foamable composite composed of the polypropylene resin composition according to the present invention, foaming agent (propellant) and, on requirement, foaming nucleating agent, organic peroxide, cross linking assistant and so on.
As the foaming agent, chemicals which exist as liquid or solid at normal temperature and develop a gas by heating can be used. Concretely, there may be employed, for example, azodicarbonamide, barium azodicarboxylate, N,Nxe2x80x2-dinitrosopentamethylenetetramine, 4,4-oxybis(benzenesulfonylhydrazide), diphenylsulfon-3,3-disulfonylhydrazide, p-toluenesulfonyl semicarbazide, trihydrazinotriazine, biurea and zinc carbonate. Among them, preference is given to compounds which develop a large amount of gas and has a gas development cease temperature sufficiently lower than the starting temperature of thermal deterioration of the polypropylene resin composition, for example, azodicarbonamide, N,Nxe2x80x2-dinitrosopentamethylenetetramine and trihydrazinotriazine. These foaming agents may preferably be present in the polypropylene resin composition in a proportion of, favorably, 1-20 parts by weight, preferably 2-5 parts by weight, per 100 parts by weight of the polypropylene resin composition.
Foaming agents other than the above may also be employed, for example, gases existing in gas phase at normal temperature and normal pressure, such as carbon dioxide, nitrogen, argon, helium, propane, butane, chlorofluorocarbons (flons), methane, ethane, oxygen and air; low boiling volatile foaming agents (low boiling organic solvents), such as n-pentane, iso-pentane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, methanol, ethanol, 1-butanole, 3-pentanol, acetone, methyl ethyl ketone and diethyl ether. Among them, preference is given to carbon dioxide and nitrogen.
The nucleating agent for the foaming is used to control the diameter and number of gas bubbles of the foamed article. Concrete examples of the foaming nucleating agent include talc, sodium bicarbonate, citric acid, calcium carbonate and ammonium carbonate.
The organic peroxide mentioned above is used for attaining cross-linking of the foamed product. As the organic peroxide, there may be employed in most cases organic peroxides and organic peroxyesters. Concrete examples therefor include the following compounds:
3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, succinic acid peroxide, acetyl peroxide, tert-butyl peroxy(2-ethyl hexanoate), m-toluoyl peroxide, benzoyl peroxide, tert-butyl peroxyisobutyrate, 1,1-bis(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxymaleate, tert-butylperoxylaurate, tert-butylperoxy-3,5,5-trimethylcyclohexanoate, cyclohexanone peroxide, tert-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxyacetate, 2,2-bis(tert-butylperoxy)butane, tert-butylperoxybenzoate, n-butyl-4,4-bis(tert-butylperoxy)valerate, di-tert-butylperoxyisophthalate, methyl ethyl ketone peroxide, xcex1,xcex1xe2x80x2-bis(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butylcumyl peroxide, diisopropylbenzene hydroperoxide, di-tert-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, cumene hydroperoxide and tert-butyl-hydroxy peroxide.
Among them, preference is given to 1,1-bis(tert-butylperoxy)cyclohexane, tert-butylperoxy maleate, tert-butylperoxy laurate, tert-butylperoxy-3,5,5-trimethyl cyclohexanoate, cyclohexanone peroxide, tert-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxy acetate, 2,2-bis(tert-butylperoxy)butane, tert-butylperoxy benzoate, n-butyl-4,4-bis(tert-butylperoxy) valerate, di-tert-butylperoxy isophthalate, methyl ethyl ketone peroxide, xcex1,xcex1xe2x80x2-bis(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butylcumyl peroxide, diisopropylbenzene hydroperoxide, di-tert-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydro peroxide, cumene hydroperoxide and tert-butylhydroxy peroxide. The organic peroxide may favorably be used in an amount of 0.01-5 parts by weight, preferably 0.01-1 part by weight, per 100 parts by weight of the polypropylene resin composition.
The cross linking assistant functions such that a hydrogen atom in the polypropylene is drawn out by the organic peroxide and the thereby produced polymer radical will react with the cross linking assistant before it comes to cleavage to thereby stabilize the polymer radical and, at the same time, to increase the cross linking efficiency. As the cross linking assistant functioning as above, there may be used usually unsaturated compounds having one or two or more double bonds, oximes, nitroso compounds and maleimides each solely or in a combination of two or more of them.
As the crosslinking assistant, there may be enumerated concretely, for example, divinyl compounds, such as divinylbenzene and diallyl phthalate; polyfunctional methacrylates and acrylates, such as 1,6-hexanediol dimethacrylate, ethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate and neopentylglycol diacrylate; cyanurates and isocyanurates, such as triallyl cyanurate and triallyl isocyanurate; oximes, such as quinone dioxime and benzoquinone dioxime; nitroso compounds, such as p-nitrosophenol and the like; and maleimides, such as N,N-methaphenylenebismaleimide and so on. Among them, preferance is given to 1,6-hexanediol dimethacrylate and neopentylglycol diacrylate.
The foamed article according to the present invention may have any shape. It may be present in a form of, for example, block, sheet and monofilament. For producing the foamed article according to the present invention using the polypropylene resin composition according to the present invention, known foam-molding apparatus can be used. The molding conditions may also be known ones.
For example, a foamed article in a form of sheet can be obtained by blending the polypropylene resin composition according to the present invention, a foaming agent which is present in liquid or solid state at normal temperature and which develops a gas by heating, an organic peroxide, a cross linking assistant and, if necessary, a heat stabilizer on a mixing apparatus, such as Henschel mixer, V-blender, ribbon blender or tumbler blender, kneading the resulting blend using an extruder, preferably that provided with a gas bent, while heating it at a temperature at which the organic peroxide will be decomposed but not the foaming agent and while removing the unnecessary volatile substances via the bent which is disposed at a portion downstream the high temperature heating zone and extruding the molten blend through a T-die or a circular die arranged on the extruder to thereby obtain a foamable sheet which contains the foaming agent in substantially undecomposed state and which has been subjected to cross linking. This foamable sheet is then brought into foaming by a known foaming technique, for example, press foaming in which the foaming agent is decomposed under a pressurized condition, a heat foaming in a molten salt bath in which the foaming agent is decomposed by heating under normal pressure, heat foaming in a hot blast oven, heat foaming by thermal radiant ray, heat foaming by microwave or combination of these techniques, to obtain a foamed article.
In an alternative method for producing a foamed article, a substantially foamed sheet can be obtained by blending the polypropylene resin composition according to the present invention, a foaming agent which is present in liquid or solid state at normal temperature and which develops a gas by heating and, if necessary, a heat stabilizer and so on, on a mixing apparatus, such as Henschel mixer, V-blender, ribbon blender or a tumbler blender, kneading the resulting blend using an extruder, while heating it at a temperature at which the foaming agent will be decomposed, and extruding the molten blend through a T-die or a circular die arranged on the extruder.
In a further alternative method for producing a foamed article, a foamed sheet can be produced by blending the polypropylene resin composition according to the present invention, a foaming nucleating agent and, if necessary, a heat stabilizer and so on, on a mixing apparatus, such as Henschel mixer, V-blender, ribbon blender or a tumbler blender, kneading the resulting blend using an extruder, while supplying continuously thereto a gas which is present at normal temperature and normal pressure in gas phase or a low boiling volatile foaming agent (low boiling organic solvent) via a nucleating agent feed nozzle disposed midway in the extruder cylinder and extruding the kneaded mass through a T-die or a circular die arranged on the extruder into a substantially foamed sheet.
By the method for producing the foamed article using a gas which exists in gas phase at normal temperature and normal pressure or a low boiling volatile foaming agent as described above, a foamed sheet having a fine foam cell structure of high foaming magnification ratio of, for example, at least 2-fold, with an average foam cell diameter of about 100 xcexcm can be obtained. When a conventional polypropylene resin or a polypropylene resin composition other than the polypropylene resin composition according to the present invention is used as the starting resin, it is difficult to obtain a foamed sheet of a high foaming magnification ratio. Thus, for example, it is difficult to obtain a foamed sheet having a foaming magnification ratio of at least 2-fold and a fine foam cell structure with an average foam cell diameter of about 100 xcexcm.
In a further alternative method for producing a foamed article, the polypropylene resin composition according to the present invention and, on requirement, heat stabilizer and so on are kneaded on a mixing apparatus, such as Henschel mixer, V-blender, ribbon blender or a tumbler blender, and the resulting blend is kneaded using an extruder to obtain a pelletized product. This pelletized product and a low boiling volatile foaming agent (low boiling organic solvent) are treated in a high-pressure vessel at a high temperature to obtain impregnated beads. The resulting impregnated beads are heated by hot steam to cause a preliminary foaming in order to adjust the diameter of the prefoamed cell, whereupon the so treated beads are transferred to a ripening process step for restoring the internal pressure of the beads to normal pressure and are contacted with air sufficiently. The resulting ripened beads are then heated in a mold by, for example, hot steam, to cause final foaming to obtain foamed article.
Concrete examples of the foamed article according to the present invention include office supplies, such as file cases; automobile inertia furnishings, such as roof liner and so on; and others, such as trays, trays for food products, cups for noodles, lunch boxes, containers for fast foods, containers for retorts, vessels for frozen foods, vessels for cooked foods, heat resistant vessels for electronic oven, cups, synthetic timber, original rolled product of various foamed sheets, shock absorbers, heat insulators, sound insulators and vibration damping material.
For molding formed articles, such as blow-molded articles, vacuum- or pressure formings, calendered articles, extrusion-molded articles, stretched films, inflation films and various foamed articles using the first or the second polypropylene resin composition according to the present invention, the starting polypropylene resin composition may favorably contain at least one stabilizer among phenolic stabilizer, organophosphite stabilizer, thioether stabilizer, hindered amine stabilizer and higher fatty acid metal salts. Such additives may favorably be used each in an amount of 0.005-5 parts by weight, preferably 0.01-0.5 part by weight per 100 parts by weight of the polypropylene resin composition according to the present invention.
As described above, the first polypropylene resin composition according to the present invention has, due to the material properties specified, a high melt tension and are superior in the moldability and can afford to process into formed articles which have better appearance and high stiffness and which are scarcely subject to deformation, even for large-sized articles, efficiently at high speed.
The second polypropylene resin composition according to the present invention has, due to the material properties specified, a high melt tension and are superior in the moldability and can afford to process into formed articles which have better appearance and high stiffness and which are scarcely subject to deformation, even for large-sized articles, efficiently at high speed.
By the process for producing the polypropylene resin composition according to the present invention, the polypropylene resin composition described above can be produced in a simple and efficient manner at a low cost, based on the fact that, in the first polymerization stage, a high molecular weight polypropylene product having an intrinsic viscosity [xcex7] of 8-13 dl/g is produced up to a definite yield and, in the second and subsequent polymerization stages, polymerization of propylene is effected in such a way that a polypropylene product having an intrinsic viscosity [xcex7] of lower than 8 dl/g is produced and the melt flow rate (MFR) of the finally obtained polypropylene resin composition as a whole will be in the range of 0.01-5 g/10 min.
The resin composition for blow molding according to the present invention can afford to process into blow-molded articles which have a better appearance and are scarcely subject to deformation even for large-sized articles, in an efficient manner at high speed, since it contains the first or the second polypropylene resin composition described above.
The blow-molded article according to the present invention is obtained by blow-molding the above-mentioned resin composition and, therefore, the parison will scarcely suffer from occurrence of draw-down, so that the blow-molded article is obtained efficiently at high speed and, in addition, is better in the appearance and difficultly deformable.
The vacuum- or pressure-formed article according to the present invention is produced by a vacuum- or pressure forming of the polypropylene resin composition described above, so that it may be permitted to be produced as a large-sized article in a high-speed production and to be processed by deep drawing and, in addition, it is superior in the stiffness and in the appearance.
The calendered article according to the present invention is produced by subjecting the polypropylene resin composition described above to a calendering, so that it may be permitted to be produced as a large-sized article and by high speed calendering and, in addition, it has scarce thickness irregularity and is superior in the gloss, in the appearance and in the stiffness.
The extruded article according to the present invention is produced by subjecting the polypropylene resin composition described above to an extrusion molding, so that it may be permitted to be produced as a large-sized article and in a high speed molding and, in addition, it is superior in the appearance and in the stiffness.
The stretched film according to the present invention is produced by subjecting a sheet or film made of the polypropylene resin composition described above to stretching, so that it may be permitted to be produced as a large-sized article and in a high speed stretching and, in addition, it can be obtained by a stable stretching without suffering from breaking of the film during the stretching and is also superior in the thickness accuracy.
The inflation film according to the present invention is produced by subjecting the polypropylene resin composition described above to an inflation molding, so that it may be permitted to be produced as a large-sized article and by a high speed molding and, in addition, it is obtained from a baloon held in a stable state and, therefore, is superior in the appearance and also in the stiffness and transparency.
Due to the fact that the foamed article according to the present invention is produced by subjecting the polypropylene resin composition described above to foaming, it may be permitted to be produced as a large-sized article and by a high speed molding and, in addition, it may be present as a foamed article having a fine and uniform foam cell structure of high foaming magnification ratio.